Stepper motors are typically used in automotive instrument clusters to convey information such as vehicle speed, engine RPM, fuel level, and engine temperature to the driver. The stepper motor is open loop controlled, i.e. a signal is applied to the motor to move it but the absolute position is not known at any one time. In order to know the position of the stepper motor, a referencing operation is required.
Original methods of seeking a reference position in a stepper motor consisted of moving the motor towards a reference point at a certain velocity for a predefined period of time to ensure that the stepper motor with an attached pointer has reached a zero position. Then the motor can be positioned using a series of command sequences designed not to lose position in the stepper motor. One of the issues with this method is that if the pointer is near the pointer stop then the pointer has a tendency to bounce off of the pointer stop.
With the advent of back ElectroMotive Force (EMF) detection, the pointer stop reference position can be detected by watching for the back EMF signal to be reduced below a predetermined level. In order to provide accurate reference detection, the rotational velocity used with this method can still be slow (under 100 degrees per second) and time consuming.
It would be desirable to have a detector device and a method for detecting a stall condition in a stepper motor, wherein the detector device and method provide a means for high speed stepper motor stall detection using rotational velocities of the stepper motor in the range of 200 to 300 degrees per second.